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Round pin sockets for 12V


aracer

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On the boat I bought recently I have round pin 3 pin sockets for 12V supply. However having been proactive and bought 5A plugs for them before I picked up the boat, I found they are actually the smaller 2A ones. Given I'd like to run stuff which uses more than 24W from this power should I upgrade the sockets or will they work OK with a bit more than 2A? I'd rather not spend money on changing all the sockets if I don't have to.

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13 minutes ago, aracer said:

On the boat I bought recently I have round pin 3 pin sockets for 12V supply. However having been proactive and bought 5A plugs for them before I picked up the boat, I found they are actually the smaller 2A ones. Given I'd like to run stuff which uses more than 24W from this power should I upgrade the sockets or will they work OK with a bit more than 2A? I'd rather not spend money on changing all the sockets if I don't have to.

It’s not just about the sockets though, it is also about the wiring and the fusing. (Theoretically at least) the fuse should take into account the lowest common denominator, so if the wiring can take 6A and the socket is rated at 2A, the fuse should be 2A. If the wiring can take 1A and the socket 2A, the fuse should be 1A. That is the theory! In practice, who knows!

 

Being practical about it I’d try the load you want, whilst monitoring the plug/socket temperature (and of course whether or not the fuse blows!)

 

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13 minutes ago, nicknorman said:

It’s not just about the sockets though, it is also about the wiring and the fusing. (Theoretically at least) the fuse should take into account the lowest common denominator, so if the wiring can take 6A and the socket is rated at 2A, the fuse should be 2A. If the wiring can take 1A and the socket 2A, the fuse should be 1A. That is the theory! In practice, who knows!

 

Being practical about it I’d try the load you want, whilst monitoring the plug/socket temperature (and of course whether or not the fuse blows!)

 

Hmm - I should have a proper check of what fuses I have on what circuits - something I've not yet got around to. I'd like to connect a laptop charger which is rated at 80W (I suppose "a bit more" was the wrong phrase, that's more than 6A!) At some point I might do a full rewire - the rewiring is something I'm really happy with, just not keen on all the dismantling of the panelling required.

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2 minutes ago, aracer said:

Hmm - I should have a proper check of what fuses I have on what circuits - something I've not yet got around to. I'd like to connect a laptop charger which is rated at 80W (I suppose "a bit more" was the wrong phrase, that's more than 6A!) At some point I might do a full rewire - the rewiring is something I'm really happy with, just not keen on all the dismantling of the panelling required.

Pull a socket or two and check the cabling behind them.  To avoid voltage drop over the run they might have been fitted with cable that can take a lot more than 2A, so you could just change the sockets.

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38 minutes ago, aracer said:

Hmm - I should have a proper check of what fuses I have on what circuits - something I've not yet got around to. I'd like to connect a laptop charger which is rated at 80W (I suppose "a bit more" was the wrong phrase, that's more than 6A!) At some point I might do a full rewire - the rewiring is something I'm really happy with, just not keen on all the dismantling of the panelling required.

Just to mention that a lot of these modern devices are “fixed power” types. So they will take (in this case) 80w regardless (within reason) of the supply voltage. So if you get 12v at the socket which is at the end of the wiring, it will take 6.66 A. But on the other hand, if the voltage has dropped to 10v at the socket which is at the end of the wiring, due to thin cable, it will take 8A. Which of course makes the voltage drop worse!

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Good point - thanks. It's a cheapish switch mode power supply (I've not had it apart, but that's undoubtedly the case given the step up voltage and light weight hence no big transformers), hence it will certainly work like that. These are things I should know a lot about, but do sometimes need reminding!

 

I've unscrewed one of the sockets to have a look and the wire looks the sort of gauge I'd normally think fine for those sort of currents - though I guess given the length of run that it needs to be thicker than I'd normally use. Too late tonight to do the calcs, I'll look into it properly tomorrow. A somewhat surprising finding though that the one I unscrewed in the dinette appears to the end of the 12V run, but fed from the front of the cabin which is only a few metres away at this point - I'd assumed there was a 12V run down each side, but it seems there is a loop going around the end (I suppose that kind of makes sense). That does explain the different voltage readings I'd got in the different sockets which had confused me!

 

It does occur to me that it might be possible to pull new wiring through without dismantling the panelling - though I think I might be doing a lot of unscrewing of stuff in the next day or two anyway as I really need to work out exactly how and where everything runs (plumbing as well as electrics). I'm also wanting to wall mount a TV and I'd feel far happier if I can take that panel off and bolt right through to the back with proper washers rather than rely on wood screws as it's a fairly big TV.

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As others have said, the current limit will depend on fusing, wire, current draw and acceptable coltage drop as well as the connector. If you do decide to change the sockets, then there are others to consider aside from 5A round pin. As long as they will take the current and there is no risk of being confused with mains sockets, then you have some choice.

I originally used car 12V, fag lighter style sockets, but thought them flimsy and easy to dislodge. Changed them for 2 pin Speakon sockets. Usually used for audio equipment, bit can take 40A. I don't have any audio equipment that uses them, so no risk of blowing something up! The plugs latch in, so very secure.

 

Jen

https://en.m.wikipedia.org/wiki/Speakon_connector

IMG_20181115_102122.jpg

Edited by Jen-in-Wellies
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I suspect that those 2A plugs and sockets would actually be fine with a much higher current, and are called ‘2A’ purely because that’s what that spur should have been fused at in the house in which they were intended to be fitted. However, as there are no specs for them showing a higher current nobody knows. 

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32 minutes ago, pig said:

The sockets are rated 2 Amps at 240 Volts; i.e. 480 Watts. Surely this means 40 Amps at 12 Volts?

No only the current is relevant. Current causes heating when passed through a connector, circuit voltage doesn’t. Which is why power sent through the national grid is very high voltage and thus relatively low current.

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Obtuse thought

If you rewire the system so that the -ve is on the large (earth) pin and the +ve is wired to both of the other two pins then you should have a larger contact area and, providing the wiring is up to it, allowing more current to be safely drawn through the connector.

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10 minutes ago, Loddon said:

Obtuse thought

If you rewire the system so that the -ve is on the large (earth) pin and the +ve is wired to both of the other two pins then you should have a larger contact area and, providing the wiring is up to it, allowing more current to be safely drawn through the connector.

Problem with that is when an unsuspecting new owner wires up his new appliance 'correctly' and wonders "Why ………………….."

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25 minutes ago, WotEver said:

 

I suspect that those 2A plugs and sockets would actually be fine with a much higher current, and are called ‘2A’ purely because that’s what that spur should have been fused at in the house in which they were intended to be fitted. However, as there are no specs for them showing a higher current nobody knows. 

That's what I was thinking, hence the question - and whilst I'm an electronic engineer I'm not quite sure how to rate a connector. Though my instincts suggest they should be fine for much higher currents if I compare them with some of the connectors used on RC cars and planes - or to use a more common example most people will be familiar with, micro USB connectors are commonly used to carry up to 2A and the contact area on those is a fraction of that on these 2A plugs.

20 minutes ago, nicknorman said:

No only the current is relevant. Current causes heating when passed through a connector, circuit voltage doesn’t. Which is why power sent through the national grid is very high voltage and thus relatively low current.

That's more to do with voltage drop from my understanding, though clearly the two issues are related (and in this case any voltage drop will be more significant at 12V than 240V - though I'm more concerned about heating for the connectors from a safety POV).

6 minutes ago, Alan de Enfield said:

Problem with that is when an unsuspecting new owner wires up his new appliance 'correctly' and wonders "Why ………………….."

Yeah - I don't think I'm going there. Though to be fair it wouldn't be a major issue that way round as they just wouldn't get any power - it would be an issue if I connected one of my plugs to a normal system (not that 2A plugs are that common I'm assuming - I think the standard is 5A).

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30 minutes ago, aracer said:

I'm not quite sure how to rate a connector.

An unscientific test would be to bench test them with a fixed current of say 5A, 10A, 15A... and measure the temperature rise. If it’s insignificant at 5A but noticeable at 10A then you’ve kinda got your answer.

 

I’ve seen plenty of overheated 13A plugs and sockets feeding washing machines and kettles over the years, so it’s not an insignificant consideration. I guess it largely depends not only on the contact area but also the design of the contacts. 

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44 minutes ago, aracer said:

 

That's more to do with voltage drop from my understanding, though clearly the two issues are related (and in this case any voltage drop will be more significant at 12V than 240V - though I'm more concerned about heating for the connectors from a safety POV).

 

Voltage drop is the same as power loss. Current down the wires doesn’t (can’t) change, high voltage at one end, lower voltage at the other = power loss dissipated as heat. Presuming the resistance of the grid, or cable, or 2A connector, is a fixed value, the power dissipated as heat is proportional to the square of the current and nothing to do with the system voltage. I^2R. Note the square term! In layman’s terms if you double the current you double the I in the VI formula for power and if you double the current across a fixed resistance you double the voltage drop, ie double the V in the VI formula too. Hence the square.

 

System voltage drop affects the end using device, or if it’s constant power increases the current. Wastes power anyway. But the connector rating, like a cable rating, is about the heating effect from the current flowing through it and its resistance. As you say, modern materials allow low resistance connections that can pass high current for the size. Old fashioned 2 A mains connectors made of brass suffer from high contact resistance even when new, and higher still as they get a bit corroded, which generates heat.

Edited by nicknorman
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46 minutes ago, WotEver said:

 

I’ve seen plenty of overheated 13A plugs and sockets feeding washing machines and kettles over the years, so it’s not an insignificant consideration. I guess it largely depends not only on the contact area but also the design of the contacts. 

 

Another reason for 13A plug tops overheating is poor connection of the wires into the screw fixings inside the plug top. 

 

This is why appliances nowadays come with factory-wired plug tops. Consumers can't be trusted to fit them correctly. 

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7 minutes ago, Boater Sam said:

13A plugs overheat the line pin due to poor fuse contacts not pin to socket contact.

Not always. I’ve seen sockets that were brown around both the live and neutral entries. 

 

It’s a dead giveaway when it’s only the line side that’s brown though. 

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16 minutes ago, Mike the Boilerman said:

 

Another reason for 13A plug tops overheating is poor connection of the wires into the screw fixings inside the plug top. 

 

This is why appliances nowadays come with factory-wired plug tops. Consumers can't be trusted to fit them correctly. 

Absolutely. I can’t remember the number of times I’ve been round someone’s house to help them out and they’ve lent me a drill or whatever and I’ve said “Before I do anything else, let’s just attach this plug properly!”

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1 hour ago, WotEver said:

I’ve seen plenty of overheated 13A plugs and sockets feeding washing machines and kettles over the years, so it’s not an insignificant consideration. I guess it largely depends not only on the contact area but also the design of the contacts. 

Quite apart from the issue of poor contact to an internal fuse, it has always been my understanding that the "square" pins in a 13A mains plug make the connection between plug and socket less reliable than was the case with old round pin plugs.  I once saw them referred to as one if the worst bits of design of the 20th century.

 

For a start the contact is usually only to a relatively small are and on just two of the flats.

By comparison the old round pin plugs have a round pin into exanding cylinder approach, and the contact is over a much larger are of the pin, (if it' all working well!)

 

in my experience the round pin 5A plugs are good for far more that 5A without significant volts drop, (and hence heating of the plug).

If it were me, I would always chose the 5 amp, rather than 2 amp size, as the contact area is a lot greater, and the holes where the conductors go will take larger flex.

The price of 5A sockets is quite low (if you buy on e-Bay or at Toolstation - maybe not in Midland Chandlers!), so swapping over to a larger size doesnt need to cost the earth.

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22 minutes ago, Mike the Boilerman said:

 

Another reason for 13A plug tops overheating is poor connection of the wires into the screw fixings inside the plug top. 

 

This is why appliances nowadays come with factory-wired plug tops. Consumers can't be trusted to fit them correctly. 

For high current appliances, it was better to use a plug-top where the connecting wires have a larger contact area with the pins. Like this:

 

mk_plug_inside.jpg.1865f6e3b2b75b5ed734c0b90c2be9a5.jpg

 

Rather than the type where the wire is poked though a hole, and held down by the screw.  Like this

 

how-to-wire-a-plug10.jpg.8f312add893a2747afd1f2f62839725d.jpg

 

 

 

 

 

 

 

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9 minutes ago, alan_fincher said:

... the contact is usually only to a relatively small are and on just two of the flats.

By comparison the old round pin plugs have a round pin into exanding cylinder approach, and the contact is over a much larger are of the pin,

I’d agree with that. Spotlights in the theatre all use 16A round pin plugs and sockets for two reasons - you don’t want a fuse blowing every time the lamp burns out, and possibly more important, they’re dead reliable. 

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